Step 2: In a medium-sized saucepan, melt together over low heat the unsalted butter, and the semi-sweet, unsweetened, and bitter-sweet chocolate. Stir constantly to prevent the chocolate from scorching.

Step 3: When just melted, remove from heat. Stir in the sugar.

Step 4: Beat in the eggs one at a time.

Step 5: Stir in the vanilla.

Step 6: Gently stir the flour and baking powder.

Step 7: Pour into the pan.

Step 8: Bake for 21 minutes. (The brownies should be slightly underdone, since they continue to cook after they’ve been removed from the pan.)

Step 9: Cool on a wire rack in the pan. Cut into squares.

Step 10: Store in an airtight container up to three days, if they last that long.